Electronic device and method of making same

ABSTRACT

The present invention provides an electronic device with improved characteristics and a method of making the electronic device. In a method of making an electronic device (piezoelectric device)  74  according to the present invention, an outer edge R 1  of a piezoelectric film  52 A formed on an electrode film  46 A of a laminate  60  is located inside an outer edge R 2  of the electrode film  46 A. For this reason, in removal of a monocrystalline Si substrate  14  from a multilayer board  61 , where an etching solution permeates between polyimide  72  and laminate  60 , the etching solution circumvents the electrode film  46 A before it reaches the piezoelectric film  52 A. Namely, a route A of the etching solution to the piezoelectric film  52 A is significantly extended by the electrode film  46 A. In the method of making the electronic device  74 , therefore, the etching solution is less likely to reach the piezoelectric film  52 A. It significantly suppresses a situation of dissolution of the piezoelectric film  52 A and realizes improvement in characteristics of the piezoelectric device  74  made.

This is a Divisional of application Ser. No. 11/360,394 filed Feb. 24,2006, which in turn claims the benefit of Japanese Patent ApplicationNo. 2005-172477, filed Jun. 13, 2005. The entire disclosure of the priorapplications are hereby incorporated by reference herein its entirety.

BACKGROUND

1. Field of the Invention

The present invention relates to an electronic device with a multilayerstructure and a method of making the same.

2. Related Background Art

There are conventional thin-film piezoelectric elements being a type ofelectronic devices in this technical field, for example, as disclosed inJapanese Patent Application Laid-Open No. 2003-229611 and others. Forfabricating the thin-film piezoelectric element described in thisApplication, two silicon substrates are first prepared and a (200) planepreferentially oriented MgO film is deposited on a surface of eachsubstrate. Then a first electrode film, a piezoelectric film, and asecond electrode film are successively laid on each substrate with theMgO film thereon, thereby fabricating two multilayer substrates. Thenthese multilayer substrates are bonded to each other with an adhesive sothat their electrode films face each other. Thereafter, only one siliconsubstrate is removed by etching. Then forming into a predeterminedelement shape by dry etching or the like and coating with resin,thereafter, the other silicon substrate is removed by etching tocomplete fabrication of the thin-film piezoelectric element. Relatedtechnologies are also disclosed in Japanese Patent ApplicationsLaid-Open No. 2002-164586, Laid-Open No. 2001-313429, and Laid-Open No.11-312801, and Japanese Patent No. 3310881.

However, the aforementioned conventional electronic device has thefollowing problem. Namely, the step of removing the second substrate byetching sometimes involved permeation of an etching solution through ajoint between the coating resin (protecting film) and the laminatecomprised of the electrode films and piezoelectric films. If thisetching solution permeates up to the piezoelectric film, thepiezoelectric film will be dissolved to heavily degrade thecharacteristics of the piezoelectric element fabricated. It also leadsto reduction of yield and reduction of productivity of the electronicdevice.

The present invention has been accomplished to solve the above problemand an object of the present invention is therefore to provide anelectronic device with improved characteristics and a method of makingthe electronic device.

SUMMARY

The method of making an electronic device according to the presentinvention is a method of making an electronic device by removing with anetching solution a substrate from a multilayer board having a laminateto become the electronic device formed on the substrate, the methodcomprising: a step of depositing on the substrate, the laminatecomprising a first thin film, and a second thin film being formed on thefirst thin film and more likely to be dissolved in the etching solutionthan the first thin film; a step of forming a protecting film to coverthe laminate; and a step of removing the substrate from the multilayerboard, using the etching solution, wherein in the step of depositing thelaminate, the second thin film is deposited so that an outer edge of thesecond thin film is located inside an outer edge of at least a portionof the first thin film.

In this method of making the electronic device, the outer edge of thesecond thin film formed on the first thin film of the laminate islocated inside the outer edge of at least a portion of the first thinfilm. For this reason, when the etching solution permeates between theprotecting film and the laminate in the removal of the substrate fromthe multilayer board, the etching solution circumvents the first thinfilm before arrival at the second thin film, in the marginal regionwhere the outer edge of the second thin film is located inside the outeredge of the first thin film. Namely, the path of the etching solution tothe second thin film is significantly extended by the first thin film.It is noted herein that in the conventional method of making theelectronic device the first thin film and the second thin film are madewith their outer edges approximately coinciding with each other and thusthe etching solution directly reaches the second thin film, withoutcircumventing the first thin film. In the method of making theelectronic device according to the present invention, therefore, thepath of the etching solution to the second thin film is extended,whereby the etching solution is less likely to reach the second thinfilm. It significantly suppresses the situation of dissolution of thesecond thin film to achieve improvement in the characteristics of theelectronic device fabricated. In addition, avoidance of dissolution ofthe second thin film also leads to improvement in the yield andproductivity of this electronic device. The deposition (film formation)in the present invention is assumed to encompass not only a process ofdepositing a film material on a predetermined substrate to form a film,but also a process of forming a film and thereafter shaping (patterning)the film.

The method of making an electronic device according to the presentinvention is a method of making an electronic device by removing with anabrasive containing a liquid a substrate from a multilayer board havinga laminate to become the electronic device formed on the substrate, themethod comprising: a step of depositing on the substrate, the laminatecomprising a first thin film, and a second thin film being formed on thefirst thin film and more likely to be dissolved in the abrasive than thefirst thin film; a step of forming a protecting film to cover thelaminate; and a step of removing the substrate from the multilayerboard, using the abrasive, wherein in the step of depositing thelaminate, the second thin film is deposited so that an outer edge of thesecond thin film is located inside an outer edge of at least a portionof the first thin film.

In this method of making the electronic device, the outer edge of thesecond thin film formed on the first thin film of the laminate islocated inside the outer edge of at least a portion of the first thinfilm. For this reason, when the abrasive permeates between theprotecting film and the laminate in the removal of the substrate fromthe multilayer board, the abrasive circumvents the first thin filmbefore arrival at the second thin film, in the marginal region where theouter edge of the second thin film is located inside the outer edge ofthe first thin film. Namely, the path of the abrasive to the second thinfilm is significantly extended by the first thin film. It is notedherein that in the conventional method of making the electronic devicethe first thin film and the second thin film are made with their outeredges approximately coinciding with each other and thus the abrasivedirectly reaches the second thin film, without circumventing the firstthin film. In the method of making the electronic device according tothe present invention, therefore, the path of the abrasive to the secondthin film is extended, whereby the abrasive is less likely to reach thesecond thin film. It significantly suppresses the situation ofdissolution of the second thin film to achieve improvement in thecharacteristics of the electronic device fabricated. In addition,avoidance of dissolution of the second thin film also leads toimprovement in the yield and productivity of this electronic device.

Preferably, in the step of depositing the laminate, the second thin filmis deposited so that the outer edge of the second thin film is locatedinside an entire outer edge of the first thin film. In this case, theetching solution or abrasive circumvents the first thin film beforearrival at the second thin film, in the entire marginal region of theouter edge of the second thin film, whereby the second thin film of theelectronic device becomes far less likely to be dissolved.

Preferably, the laminate includes a multilayer structure in which apiezoelectric film is interposed between a pair of electrode films; thefirst thin film is one of the electrode films, and the second thin filmis the piezoelectric film. Furthermore, preferably, the laminateincludes a multilayer structure in which a piezoelectric film isinterposed between a pair of electrode films, and includes an oxide filminterposed between the substrate and the electrode film closer to thesubstrate out of the pair of electrode films; the first thin film is theoxide film, and the second thin film is the piezoelectric film. In thesecases, dissolution of the piezoelectric film being the second thin film,with the etching solution is significantly suppressed and apiezoelectric device is obtained with excellent piezoelectriccharacteristics.

Preferably, in the step of forming the protecting film, the protectingfilm is formed in a plurality of separate stages. In this case, thesecond and subsequent formation of the protecting film allows us toadjust the size of the protecting film or to change the constituentmaterial of the protecting film and it is thus feasible to achievediversification of the protecting film.

An electronic device according to the present invention is an electronicdevice obtained by removing with an etching solution a substrate from amultilayer board having a laminate to become the electronic deviceformed on the substrate, wherein the laminate has one surface and sideface covered by a protecting film and another surface exposed from theprotecting film and comprises a first thin film, and a second thin filmbeing located on the one surface side of the first thin film and morelikely to be dissolved in the etching solution than the first thin film,and wherein an outer edge of the second thin film is located inside anouter edge of at least a portion of the first thin film.

In this electronic device, the outer edge of the second thin filmlocated on the one surface side of the first thin film of the laminateis located inside the outer edge of at least a portion of the first thinfilm. For this reason, when the etching solution permeates between theprotecting film and the laminate in the removal of the substrate fromthe multilayer board, the etching solution circumvents the first thinfilm before arrival at the second thin film, in the marginal regionwhere the outer edge of the second thin film is located inside the outeredge of the first thin film. Namely, the path of the etching solution tothe second thin film is significantly extended by the first thin film.It is noted herein that in the conventional electronic device the firstthin film and the second thin film are formed with their outer edgesapproximately coinciding with each other and thus the etching solutiondirectly reaches the second thin film, without circumventing the firstthin film. Therefore, the electronic device according to the presentinvention has the structure wherein the path of the etching solution tothe second thin film is extended so that the etching solution is lesslikely to reach the second thin film. It significantly suppresses thesituation of dissolution of the second thin film and provides theelectronic device with excellent characteristics. In addition, avoidanceof dissolution of the second thin film leads to improvement in the yieldand productivity of the electronic device.

The electronic device according to the present invention is anelectronic device obtained by removing with an abrasive containing aliquid a substrate from a multilayer board having a laminate to becomethe electronic device formed on the substrate, wherein the laminate hasone surface and side face covered by a protecting film and anothersurface exposed from the protecting film, and comprises a first thinfilm, and a second thin film being located on the one surface side ofthe first thin film and more likely to be dissolved in the abrasive thanthe first thin film, and wherein an outer edge of the second thin filmis located inside an outer edge of at least a portion of the first thinfilm.

In this electronic device, the outer edge of the second thin filmlocated on the one surface side of the first thin film of the laminateis located inside the outer edge of at least a portion of the first thinfilm. For this reason, when the abrasive permeates between theprotecting film and the laminate in the removal of the substrate fromthe multilayer board, the abrasive circumvents the first thin filmbefore arrival at the second thin film, in the marginal region where theouter edge of the second thin film is located inside the outer edge ofthe first thin film. Namely, the path of the abrasive to the second thinfilm is significantly extended by the first thin film. It is notedherein that in the conventional electronic device the first thin filmand the second thin film are formed with their outer edges approximatelycoinciding with each other and thus the abrasive directly reaches thesecond thin film, without circumventing the first thin film. Therefore,the electronic device according to the present invention has thestructure wherein the path of the abrasive to the second thin film isextended so that the abrasive is less likely to reach the second thinfilm. It significantly suppresses the situation of dissolution of thesecond thin film and provides the electronic device with excellentcharacteristics. In addition, avoidance of dissolution of the secondthin film leads to improvement in the yield and productivity of theelectronic device.

Preferably, the outer edge of the second thin film is located inside anentire outer edge of the first thin film. In this case, the etchingsolution or abrasive circumvents the first thin film before arrival atthe second thin film, in the entire marginal region of the outer edge ofthe second thin film, whereby the second thin film of the electronicdevice becomes far less likely to be dissolved.

Preferably, the laminate includes a multilayer structure in which apiezoelectric film is interposed between a pair of electrode films; thefirst thin film is one of the electrode films, and the second thin filmis the piezoelectric film. Furthermore, preferably, the laminateincludes a multilayer structure in which a piezoelectric film isinterposed between a pair of electrode films, and includes an oxide filminterposed between the substrate and the electrode film closer to thesubstrate out of the pair of electrode films; the first thin film is theoxide film, and the second thin film is the piezoelectric film. In thesecases, dissolution of the piezoelectric film being the second thin film,with the etching solution or abrasive is significantly suppressed and apiezoelectric device is obtained with excellent piezoelectriccharacteristics.

Preferably, the protecting film is comprised of a plurality ofprotecting films. In this case, it is easy to change the size andconstituent material of the protecting film and it is thus feasible toachieve diversification of the protecting film.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic configuration diagram showing a thin film makingsystem used in making of a piezoelectric device according to anembodiment of the present invention.

FIG. 2 is an illustration showing the first half of a procedure ofmaking the piezoelectric device according to the first embodiment of thepresent invention.

FIG. 3 is an illustration showing the second half of the procedure ofmaking the piezoelectric device according to the first embodiment of thepresent invention.

FIG. 4 is an enlarged drawing of major part of the piezoelectric deviceaccording to the first embodiment of the present invention.

FIG. 5 is a view showing a piezoelectric device in a form different fromFIG. 4.

FIG. 6 is an illustration showing the second half of a procedure ofmaking the piezoelectric device according to the second embodiment ofthe present invention.

FIG. 7 is an enlarged drawing of major part of the piezoelectric deviceaccording to the second embodiment of the present invention.

FIG. 8 is a view showing a piezoelectric device in a form different fromFIG. 7.

DETAILED DESCRIPTION OF EMBODIMENTS

A mode believed best for carrying out the electronic device and methodof making the same according to the present invention will be describedbelow in detail with reference to the accompanying drawings. Identicalor equivalent elements will be denoted by the same reference symbols,without redundant description.

Embodiments of the present invention will be described as examples ofpiezoelectric devices being a type of electronic devices.

First Embodiment

First, a making system (evaporation system) used in making of thispiezoelectric device will be described with reference to FIG. 1.

As shown in FIG. 1, the evaporation system 10 is provided with a vacuumchamber 12 and this vacuum chamber 12 is vacuated inside by an evacuator12 a. A holder 16 for holding a monocrystalline Si substrate 14 isarranged in the lower part of the vacuum chamber 12. A motor 20 isconnected through a rotational shaft 18 to this holder 16 and the holder16 is rotated by this motor 20 so that the monocrystalline Si substrate14 can be rotated in the plane of the substrate. A heater 22 for heatingthe monocrystalline Si substrate 14 is incorporated in the holder 16.

There are Zr evaporator 24, Y evaporator 26, Pt evaporator 28, Pbevaporator 30, Ti evaporator 32, and La evaporator 34 arranged below theholder 16. Each of these evaporators 24, 26, 28, 30, 32, 34 is providedwith a corresponding metal source and with an energy supply (electronbeam generator, resistance heater, or the like) for supplying energy forevaporation to the metal source.

A loop RF antenna 36 is provided between the evaporators 24, 26, 28, 30,32, 34 and the holder 16 so as to surround an emission route ofevaporated materials emitted from the evaporators 24, 26, 28, 30, 32,34. The evaporation system 10 is also provided with a gas supply 38 forsupplying an oxidizing gas, and a supply port 38 a of this gas supply 38is arranged immediately below the holder 16. For this reason, theoxidizing gas has a high partial pressure in the vicinity of themonocrystalline Si substrate 14. Collaboration of these RF antenna 36and gas supply 38 creates an environment of oxygen plasma to implement ahigh-accuracy film formation process. The oxidizing gas used in the filmformation process can be, for example, oxygen, ozone, atomic oxygen,NO₂, or the like.

Next, a procedure of making the piezoelectric device according to thefirst embodiment, using the above-described evaporation system 10, willbe described with reference to FIGS. 2 and 3.

First, a monocrystalline Si substrate 14 is set on the holder 16 of theevaporation system 10 so that a substrate surface 14 a of the (100)plane exposed faces down. Here the substrate surface 14 a is preferablyone resulting from etching cleaning of a surface of a mirror-finishedwafer. The etching cleaning is carried out with a 40% ammonium fluorideaqueous solution or the like. Since the cleaned monocrystalline Sisubstrate 14 demonstrates extremely high reactivity, it is preferablytreated by a predetermined surface treatment to protect it fromrearrangement, contamination, and so on.

Next, a ZrO₂ film 40A and a Y₂O₃ film 42A are successively epitaxiallygrown in the thickness of 0.01 μm and in the thickness of 0.04 μm,respectively, on the substrate surface 14 a of the monocrystalline Sisubstrate 14 to form an oxide film 44A (cf. part (a) in FIG. 2). Herethe ZrO₂ film 40A is an epitaxial film of zirconium dioxide (ZrO₂), andthe Y₂O₃ film 42A an epitaxial film of yttrium oxide (Y₂O₃). Morespecifically, while supplying Zr from the Zr evaporator 24 or Y from theY evaporator 26, the ZrO₂ film 40A and the Y₂O₃ film 42A are depositedon the surface 14 a of the monocrystalline Si substrate 14 heated at400° C. or higher, under the oxygen plasma environment acquired bycollaboration of RF antenna 36 and gas supply 38 described above. Thegrowth face of the ZrO₂ film 40A epitaxially grown as described abovebecomes the (001) plane, and the growth face of the Y₂O₃ film 42Abecomes the (100) plane.

Where the film formation is carried out on a large substrate area of notless than 10 cm², e.g., a large monocrystalline substrate area in thediameter of 2 inches, the monocrystalline Si substrate 14 is rotated bythe motor 20 to supply oxygen in high partial pressure to the entiresurface of the substrate, thereby enabling fabrication of film over thelarge area. At this time, the rotation speed of the substrate isdesirably not less than 10 rpm. If the rotation speed is too low, therewill occur a distribution of film thicknesses in the substrate plane.There is no particular upper limit to the rotation speed of thesubstrate, but it is normally approximately 120 rpm in view of themechanism of the vacuum system.

Next, an electrode film (first thin film) 46A is epitaxially grown inthe thickness of 0.2 μm on the oxide film 44A (cf. part (b) in FIG. 2).More specifically, Pt is supplied from the Pt evaporator 28 toward thetop surface of the monocrystalline Si substrate 14 under theaforementioned oxygen plasma environment to deposit the electrode film46A of Pt. The electrode film 46A epitaxially grown in this manner isoriented in the <100> direction.

Furthermore, a PLT film 48A and a PZT film 50A are successivelyepitaxially grown in the thickness of 0.02 μm and in the thickness of2.5 μm, respectively, on the electrode film 46A to form a piezoelectricfilm (second thin film) 52A. Here the PLT film 48A is an epitaxial filmof lead titanate doped with La (PLT), and the PZT film 50A is anepitaxial film of lead zirconate titanate (PZT). More specifically, Tifrom the Ti evaporator 32, Pb from the Pb evaporator 30, La from the Laevaporator 34, and Zr from the Zr evaporator 24 are selectively suppliedonto the top surface of the heated monocrystalline Si substrate 14 underthe aforementioned oxygen plasma environment to deposit the PLT film 48Aand PZT film 50A. Each of these PLT film 48A and PZT film 50A has itsgrowth direction (thickness direction) along the <001> direction and isc-axis singly oriented. Namely, this piezoelectric film 52A is aperovskite piezoelectric film.

Next, an electrode film 54A is epitaxially grown in the thickness of 0.2μm on the piezoelectric film 52A (cf. part (c) in FIG. 2). Morespecifically, Pt is supplied from the Pt evaporator 28 onto the topsurface of the monocrystalline Si substrate 14 under the aforementionedoxygen plasma environment to deposit the electrode film 54A of Pt.

The above completes fabrication of a first substrate 56A in which theoxide film 44A, electrode film 46A, piezoelectric film 52A, andelectrode film 54A are successively laid on the monocrystalline Sisubstrate 14. Furthermore, another substrate (second substrate 56B),which is the same as the first substrate 56A, is prepared. Namely, thissecond substrate 56B is also one in which an oxide film 44B (ZrO₂ film40B and Y₂O₃ film 42B), electrode film 46B, piezoelectric film 52B (PLTfilm 48B and PZT film 50B), and electrode film 54B, corresponding to theoxide film 44A, electrode film 46A, piezoelectric film 52A, andelectrode film 54A of the first substrate 56A, respectively, aresuccessively laid on a monocrystalline Si substrate 14.

Then the first and second substrates 56A, 56B are taken out of themaking system 10 and the first substrate 56A and the second substrate56B are bonded to each other with an adhesive so that the electrode film54A being the topmost film of the first substrate 56A is superimposed onthe electrode film 54B being the topmost film of the second substrate56B (cf. part (d) in FIG. 2).

Then the monocrystalline Si substrate 14 on one side is removed with anetching solution such as, an alkaline solution such as potassiumhydroxide, hydrofluoric acid, a hydrofluoric acid-nitric acid mixture orthe like (cf. part (e) in FIG. 2). It results in obtaining a multilayerboard 61 composed of a laminate 60 in which the electrode films 54A,54B, piezoelectric films 52A, 52B, electrode films 46A, 46B, and oxidefilms 44A, 44B are successively arranged on both sides of an adhesivefilm 58, and the monocrystalline Si substrate 14 attached to one surface60 a (which will be referred to as a substrate surface) of the laminate60. Namely, the laminate 60 is provided with two sets of multilayerstructures 62 in which the piezoelectric film 52A or 52B is interposedbetween the electrode film pair (the pair of electrode film 46A andelectrode film 54A, or the pair of electrode film 46B and electrode film54B).

Then the multilayer board 61 (i.e., the monocrystalline Si substrate 14with the laminate 60 thereon) is patterned into a size corresponding toafter-described piezoelectric device 74 and from the topmost ZrO₂ film40B to the PLT film 48A by the well-known photolithography technology(cf. part (a) in FIG. 3). This patterning determines the outer edge ofthe piezoelectric film 52A. In conjunction with this patterning, threeholes 70A, 70B, 70C reaching the electrode film 54A, electrode film 46B,and electrode film 54B, respectively, are formed in a portion of anindividual laminate 60 separated by the patterning.

Subsequently, patterning of the electrode film 46A and oxide film 44A iscarried out in the same manner as the above patterning, in the portionof the individual laminate 60 separated by the patterning (cf. part (b)in FIG. 3). This patterning is carried out so that the entire outer edgeof the electrode film 46A and oxide film 44A is located outside theentire outer edge of the piezoelectric film 52A by a predetermined widthd. This patterning results in completely separating the individuallaminate 60 to become a piezoelectric device 74, on the substrate 14. Inconjunction with this patterning, in the individual laminate 60 the hole70A is extended down to the electrode film 46A and a hole 70D extendingfrom the electrode film 54B to the electrode film 54A is formed in thebottom surface of the hole 70C.

Next, polyimide 72 is applied over the entire surface of themonocrystalline Si substrate 14 to integrally cover the top face andside face of the individual laminate 60 with polyimide (protecting film)72 and to fill the holes 70A-70D of the individual laminate 60 withpolyimide 72 (cf. part (c) in FIG. 3). Then the polyimide 72 ispatterned to determine the outer edge of polyimide 72 corresponding tothe individual laminate 60 (cf. part (d) in FIG. 3). At this time, thepolyimide 72 in the holes 70A-70C is removed by etching to the size alittle smaller than the holes 70A-70C, thereby obtaining the holes70A-70C with the inside face covered with polyimide 72, and the hole 70Dwith the inside face exposed.

Subsequently, in the individual laminate 60 Au is filled in each of theholes 70A-70D with the inside face covered by polyimide 72, to formthree vias V1, V2, V3 (cf. part (e) in FIG. 3). Namely, via V1 extendsto the electrode film 46A, and via V2 to the electrode film 46B.Furthermore, via V1 and via V2 are connected to each other on the topface of polyimide 72, and the electrode film 46A and the electrode film46B are electrically connected to each other by the via V1 and via V2.The via V3 extends to the electrode film 54A and, since the inside faceof the hole 70D is not covered by the polyimide 72, the electrode film54A and the electrode film 54B are electrically connected to each otherby this via V3.

Finally, the remaining monocrystalline Si substrate 14 is removed withan etching solution such as, an alkaline solution such as potassiumhydroxide, hydrofluoric acid, a hydrofluoric acid-nitric acid mixture orthe like (cf. part (f) in FIG. 3). It results in separating from themonocrystalline Si substrate 14 the laminate 60 in which one surface(i.e., surface 60 b opposite to substrate surface 60 a) and side face 60c are covered by the polyimide 72 and in which the other surface (i.e.,substrate surface 60 a) is exposed, and thereby obtaining apiezoelectric device 74. In use of this piezoelectric device 74, oneterminal of an ac power supply is connected through the via V1 and viaV2 to the electrode film 46A and electrode film 46B, and the otherterminal is connected through the via V3 to the electrode film 54A andelectrode film 54B.

Next, the aforementioned step of removing the second monocrystalline Sisubstrate 14 by etching in fabrication of the piezoelectric device 74will be described in more detail with reference to FIG. 4.

For separating the laminate 60 from the monocrystalline Si substrate 14,the monocrystalline Si substrate 14 is immersed in an etching solutionfrom the opposite side to the surface 14 a on which the laminate 60 isformed. More specifically, a two-sided tape is used to attach themultilayer board 61 covered with polyimide 72 and provided with the viasV1, V2, V3 to a base material (not shown) such as polyvinyl chloride sothat the top face 61 a faces the base material, and the circumference ofthis multilayer board 61 is sealed. Then the whole is immersed in theetching solution. The Inventors confirmed that on that occasion theetching solution permeated through a joint P between polyimide 72 andlaminate 60 on the substrate surface 60 a of the laminate 60 to cause asituation of dissolution of the piezoelectric film 52A.

In the piezoelectric device 74, therefore, the outer edge R1 of thepiezoelectric film 52A is located inside the outer edge R2 of theelectrode film 46A with higher resistance to dissolution in the etchingsolution than the piezoelectric film 52A. For this reason, when theetching solution permeates between the polyimide 72 and the laminate 60,it passes through a route A to significantly circumvent the electrodefilm 46A. On the other hand, in the case of the conventionalpiezoelectric device fabricated so that the outer edge of the electrodefilm 46A approximately coincides with the outer edge of thepiezoelectric film 52A, the etching solution passes through a route B tolinearly and directly reach the piezoelectric film 52A, withoutcircumventing the electrode film 46A. Namely, in the piezoelectricdevice 74 the route of the etching solution to the piezoelectric film52A is significantly extended by the electrode film 46A, and the etchingsolution is less likely to reach the piezoelectric film 52A than in theconventional piezoelectric device. For this reason, the situation ofdissolution of the piezoelectric film 52A with the etching solution issignificantly suppressed in this piezoelectric device 74 and thecharacteristics of the device are improved as compared with theconventional piezoelectric device. In addition, avoidance of dissolutionof the piezoelectric film 52A leads to improvement in the yield andproductivity of the piezoelectric device 74.

In the piezoelectric device 74, as described above, the entire outeredge R1 of the piezoelectric film 52A is located inside the outer edgeR2 of the electrode film 46A, whereby it is extremely hard for theetching solution to reach the piezoelectric film 52A. As long as atleast a part of the outer edge R1 of the piezoelectric film 52A islocated inside the outer edge R2 of the electrode film 46A, the etchingsolution circumvents the electrode film 46A in the outer edge part,thereby achieving the foregoing effect. It is, however, needless tomention that a more effective configuration is that the entire outeredge R1 of the piezoelectric film 52A is located inside the outer edgeR2 of the electrode film 46A.

The longer the distance (width) d between the outer edge R1 of thepiezoelectric film 52A and the outer edge R2 of the electrode film 46A,the less likely the etching solution is to reach the piezoelectric film52A, of course; therefore, it becomes feasible to more securely suppressthe situation of dissolution of the piezoelectric film 52A. For thisreason, the length d is more preferably not less than 10 times the totalthickness of the thickness of the oxide film 44A (0.05 μm) and thethickness of the electrode film 46A (0.2 μm). If an increase of distanced by enlargement of the electrode film 46A results in exposing theelectrode film 46A from the formed region of polyimide 72, the exposedpart of the electrode film may be covered by another polyimide 72Adifferent from the polyimide 72 (cf. FIG. 5). By adopting two polyimides72, 72A in this manner, it becomes easy to change the size andconstituent material of the protecting film and it thus becomes feasibleto achieve diversification of the protecting film. Since the protectingfilm is formed in multiple stages in formation of the protecting film,the second or subsequent formation of the protecting film permits us toadjust the size of the protecting film or to change the constituentmaterial of the protecting film, and it thus enables achievement ofdiversification of the protecting film.

Second Embodiment

Next, a procedure of making a piezoelectric device 74B according to thesecond embodiment will be described with reference to FIG. 6.

For making the piezoelectric device 74B according to the secondembodiment, the multilayer board 61 is also prepared in the sameprocedure as in the first embodiment.

Then the multilayer board 61 is patterned from the topmost ZrO₂ film 40Bto the electrode film 46A so as to achieve the size corresponding toafter-described piezoelectric device 74B, by the well-knownphotolithography technology (cf. part (a) in FIG. 6). This patterningdetermines the outer edge of the piezoelectric film 52A. In conjunctionwith this patterning, holes 70A, 70B, and 70C similar to those in thefirst embodiment are formed in the portion of individual laminate 60separated by the patterning.

Subsequently, patterning of the oxide film 44A (first thin film) iscarried out in the same manner as the above patterning, in the portionof individual laminate 60 separated by the patterning (cf. part (b) inFIG. 6). This patterning is carried out so that the entire outer edge ofthe oxide film 44A is located outside the entire outer edge of thepiezoelectric film 52A by the predetermined width d. This patterningresults in completely separating the individual laminate 60 to becomethe piezoelectric device 74B, on the substrate 14. In conjunction withthis patterning, in the individual laminate 60 the hole 70A is extendeddown to the electrode film 46A and a hole 70D extending from theelectrode film 54B to the electrode film 54A is formed in the bottomsurface of the hole 70C.

Thereafter, the application of polyimide 72 (cf. part (c) in FIG. 6),the patterning of polyimide 72 (cf. part (d) in FIG. 6), the formationof vias V1, V2, V3 (cf. part (e) in FIG. 6), and the removal ofmonocrystalline Si substrate 14 (cf. part (f) in FIG. 6) are carried outaccording to the procedure similar to that in the first embodiment, tocomplete fabrication of piezoelectric device 74B. As apparent from theabove description of the method for making, this piezoelectric device74B is different only in the piezoelectric film 46A from thepiezoelectric device 74 of the first embodiment.

Next, the step of removing the second monocrystalline Si substrate 14 byetching in the fabrication of the piezoelectric device 74B will bedescribed in more detail with reference to FIG. 7.

In the second embodiment the separation of the laminate 60 from themonocrystalline Si substrate 14 is also carried out by a method similarto that in the first embodiment. In the piezoelectric device 74B of thesecond embodiment, the outer edge R1 of the piezoelectric film 52A isarranged inside the outer edge R3 of the oxide film 44A with higherresistance to dissolution in the etching solution than the piezoelectricfilm 52A. For this reason, when the etching solution permeates betweenpolyimide 72 and laminate 60, the etching solution passes through aroute A′ to significantly circumvent the oxide film 44A. On the otherhand, in the case of the conventional piezoelectric device in which theouter edge of the oxide film 44A approximately coincides with the outeredge of the piezoelectric film 52A, the etching solution passes througha route B′ to linearly and directly reach the piezoelectric film 52A,without circumventing the oxide film 44A. Namely, the route of theetching solution to the piezoelectric film 52A is significantly extendedby the oxide film 44A in the piezoelectric device 74B, and the etchingsolution is less likely to reach the piezoelectric film 52A than in theconventional piezoelectric device. In this piezoelectric device 74B, asin the aforementioned piezoelectric devices 74, 74A, the situation ofdissolution of the piezoelectric film 52A with the etching solution isthus also significantly suppressed, and the characteristics of thedevice are improved as compared with the conventional piezoelectricdevice. In addition, avoidance of dissolution of the piezoelectric film52A also leads to improvement in the yield and productivity of thispiezoelectric device 74B.

The Inventors conducted an experiment as described below, in order tocheck the permeation of the etching solution in more detail.Specifically, we prepared piezoelectric devices 74 (samples #2) of thefirst embodiment, piezoelectric devices 74B (samples #3) of the secondembodiment, and conventional piezoelectric devices (samples #1) beforethe etching removal of the second monocrystalline Si substrate 14, 400samples each. The single crystal of SiC remaining in each piezoelectricdevice was removed by etching with the aforementioned etching solutionand thereafter permeation of the etching solution was checked by whetherthe piezoelectric layer was corroded. We calculated percentages ofpiezoelectric devices without permeation of the etching solution(permeation prevention rates). The results of the experiment were aspresented in Table 1 below.

TABLE 1 Total Permeation Number of Number of Samples Prevention Sampleswithout Corrosion Rate (%) Samples #1 400 0 0.0 Samples #2 400 232 58.0Samples #3 400 386 96.5

Namely, with the samples #1 of the conventional piezoelectric devices,permeation of the etching solution was observed in all the samples. Onthe other hand, with the samples #2 of the piezoelectric devices 74 ofthe first embodiment and the samples #3 of the piezoelectric devices 74Bof the second embodiment, there were 232 samples and 386 samples withoutpermeation, respectively. It is apparent from this result that when theroute of the etching solution to the piezoelectric film is extended asin the case of the samples #2 and #3, the permeation of the etchingsolution is obviously suppressed as compared with the conventionalpiezoelectric devices of samples #1.

Furthermore, it is also seen from Table 1 that the permeation of theetching solution is more prevented in the piezoelectric devices 74B(samples #3) than in the piezoelectric devices 74 (samples #2). This isconsidered to arise from the difference of adhesion of the electrodefilm 46A and oxide film 44A to polyimide 72. Namely, the adhesionstrength between oxide film 44A and polyimide 72 is higher than thatbetween electrode film 46A and polyimide 72, and this is a conceivablereason why the permeation prevention rate is higher in the piezoelectricdevices 74B with the wider contact region between oxide film 44A andpolyimide 72. In the case of the samples #3, it is considered that thepermeation of the etching solution can be perfectly suppressed byperforming the film formation steps and patterning steps in theproduction more accurately so as to inhibit influence of particles anddamages on the device.

Therefore, the piezoelectric device 74B of the second embodiment is ableto more securely suppress the situation of dissolution of thepiezoelectric film 52A with the etching solution than the piezoelectricdevices 74, 74A of the first embodiment.

As long as at least a part of the outer edge R3 of the oxide film 44A islocated inside the outer edge R1 of the electrode film 46A in thepiezoelectric device 74B, the etching solution also circumvents theelectrode film 46A in the outer edge part, so as to achieve theaforementioned effect. It is, however, needless to mention that a moreeffective configuration is such that the entire outer edge R1 of thepiezoelectric film 52A is located inside the outer edge R3 of the oxidefilm 44A.

In addition, the longer the distance (width) d between the outer edge R1of the piezoelectric film 52A and the outer edge R3 of the oxide film44A, the less likely the etching solution is to reach the piezoelectricfilm 52A, of course; therefore, it is feasible to more securely suppressthe situation of dissolution of the piezoelectric film 52A. For thisreason, the piezoelectric device of the second embodiment can also beconstructed as a piezoelectric device 74C covered with polyimide 72 andanother polyimide 72A (cf. FIG. 8), like the piezoelectric device 74A ofthe first embodiment.

The present invention is by no means limited to the above embodimentsbut can be modified in various ways. For example, the electronic devicesare not limited to the piezoelectric devices, but may be various deviceswith functional thin films such as dielectric films, conductor films,and semiconductor films. The number of layers in the laminate is notlimited to the aforementioned number, either. The number of layers canbe suitably selected from the numbers of layers of not less than 2(first thin film and second thin film).

The substrates are not limited to the monocrystalline Si substrates, butmay be monocrystalline substrates or polycrystalline substrates made ofmaterials different from Si. The solution to be used for removal of thesubstrates is not limited to the aforementioned etching solutions aslong as it is a liquid that can dissolve the second thin film more thanthe first thin film; for example, it may be an abrasive containing aliquid. The protecting film is not limited to polyimide, but can besuitably selected from materials with sufficiently high resistance tothe etching solution used.

The constituent material of the electrode films is not limited to Pt,but may be a material containing at least one species selected from ametal material group consisting of Au, Ir, Pd, Rh, Cu, and Ag, forexample. Furthermore, the piezoelectric film is not limited to theaforementioned configuration, but may be a c-axis singly oriented thinfilm made of lead strontium titanate or lead titanate. It is alsopossible to adopt any other making system for fabrication of thethin-film piezoelectric element; for example, it is also possible to usea sputtering system or MBE system.

The above embodiments described the methods of making electronic devices(piezoelectric devices) finally separated into individual devices, butit is also possible to adopt a configuration wherein the multilayerboard in the state shown in the part (c) in FIG. 3 or in the part (c) inFIG. 6 is bonded to a separately prepared substrate with an adhesive orthe like to obtain a plurality of electronic devices arrayed on thissubstrate.

1. An electronic device obtained by removing with an etching solution asubstrate from a multilayer board having a laminate to become theelectronic device formed on the substrate, wherein the laminate has onesurface and side face covered by a protecting film and another surfaceexposed from the protecting film, and comprises a first thin film formedof a first material, and a second thin film being located on the onesurface side of the first thin film and formed of a second materialhaving lower resistance to dissolution in the etching solution than thefirst material, and an outer edge of the second thin film is locatedinside an outer edge of at least a portion of the first thin film. 2.The electronic device according to claim 1, wherein the outer edge ofthe second thin film is located inside an entire outer edge of the firstthin film.
 3. The electronic device according to claim 1, wherein thelaminate includes a multilayer structure in which a piezoelectric filmis interposed between a pair of electrode films, and wherein the firstthin film is one of said electrode films and the second thin film is thepiezoelectric film.
 4. The electronic device according to claim 1,wherein the laminate includes a multilayer structure in which apiezoelectric film is interposed between a pair of electrode films, andincludes an oxide film interposed between the substrate and theelectrode film closer to the substrate out of the pair of electrodefilms, and wherein the first thin film is the oxide film and the secondthin film is the piezoelectric film.
 5. The electronic device accordingto claim 1, wherein the protecting film is comprised of a plurality ofprotecting films.
 6. An electronic device obtained by removing with anabrasive containing a liquid a substrate from a multilayer board havinga laminate to become the electronic device formed on the substrate,wherein the laminate has one surface and side face covered by aprotecting film and another surface exposed from the protecting film,and comprises a first thin film formed of a first material, and a secondthin film being located on the one surface side of the first thin filmand formed of a second material having lower resistance to dissolutionin the abrasive than the first material, and an outer edge of the secondthin film is located inside an outer edge of at least a portion of thefirst thin film.
 7. The electronic device according to claim 6, whereinthe outer edge of the second thin film is located inside an entire outeredge of the first thin film.
 8. The electronic device according to claim6, wherein the laminate includes a multilayer structure in which apiezoelectric film is interposed between a pair of electrode films, andwherein the first thin film is one of said electrode films and thesecond thin film is the piezoelectric film.
 9. The electronic deviceaccording to claim 6, wherein the laminate includes a multilayerstructure in which a piezoelectric film is interposed between a pair ofelectrode films, and includes an oxide film interposed between thesubstrate and the electrode film closer to the substrate out of the pairof electrode films, and wherein the first thin film is the oxide filmand the second thin film is the piezoelectric film.
 10. The electronicdevice according to claim 6, wherein the protecting film is comprised ofa plurality of protecting films.